Objective: Drug-induced lupus erythematosus is a serious side effect of certain medications, such as procainamide, quinidine, hydralazine, chlorpromazine, and isoniazid, the underlying pathogenesis of which is unresolved. In this study, we examined the influence of these drugs on the regulation of apoptosis, or programmed cell death, in quiescent and activated human lymphocytes. We also discuss the dysregulation of apoptosis as a pathogenetic factor in systemic lupus erythematosus.
Methods: Peripheral blood mononuclear cells or activated lymphoblasts from normal donors were incubated with different concentrations of each of the above-mentioned drugs.
Results: We did not find induction of apoptosis in quiescent cells over a broad concentration range. In contrast, lymphoblasts readily underwent apoptosis when cultured with chlorpromazine, but not any of the other drugs, after stimulation with interleukin-2 (IL-2) in a dose-, time- and cell cycle-dependent manner. By several lines of evidence, toxicity was ruled out. Characteristic features of apoptosis-like incorporation of propidium iodide (PI), such as increased annexin V binding, changes in mitochondrial membrane potential, and induction of DNA breaks (as evidenced by TUNEL techniques), could be induced in lymphoblasts after chlorpromazine treatment. Chlorpromazine did not cause apoptosis by inhibition of cytokine binding or blockade of early intracellular signaling. The protease inhibitor Z-VAD and the ceramide inhibitor sphingosine 1-phosphate effectively blocked chlorpromazine-induced apoptosis (by PI staining and by externalization of phosphatidylserine), in contrast to the caspase 3/CPP32 inhibitor DEVD, which had only minor effects. Western blot analysis revealed IL-2-mediated phosphorylation of extracellular signal-regulated kinase, which was sensitive to chlorpromazine. Using lymphoblasts from a patient with Canale-Smith syndrome, we found that chlorpromazine-mediated apoptosis is Fas/ APO-1 independent.
Conclusion: These data suggest that chlorpromazine mediates apoptosis in human lymphoblasts through specific activation of intracellular proapoptotic signaling cascades. This mechanism might lead to an unsynchronized inflow of apoptotic break-down products and thereby to the induction of (auto)immunity against nuclear components.